1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking an electrolyte electrode assembly and separators alternately, and providing terminal plates at opposite ends in a stacking direction of the fuel cell stack. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes. Further, the present invention relates to a method of producing the fuel cell stack.
2. Description of the Related Art
Generally, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which comprises a pair of electrodes (anode and cathode) and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is interposed between separators.
In the fuel cell, a fuel gas (reactant gas) such as a gas chiefly containing hydrogen (hydrogen-containing gas) is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte, and the electrons flow through an external circuit to the cathode, creating a DC electric current. A gas chiefly containing oxygen (oxygen-containing gas) or air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
At opposite ends of the fuel cell in a stacking direction, terminal plates for collecting electrical energy generated in the fuel cell are provided. Insulator plates are provided on the outside of the terminal plates. Further, end plates for tightening the fuel cell are provided on the outside of the insulator plates.
In the fuel cell, passages for a fuel gas, an oxygen-containing gas, and a coolant are provided. It has been pointed out that leakage of electrical energy through water produced in the power generation or a coolant may occur undesirably. In an attempt to address the problem, U.S. Pat. No. 4,371,433 discloses a technique in which sealing grommets (tubular members) such as insulating rubbers are inserted into reactant gas passages formed in bipolar plates of a fuel cell for insulating the reactant gas passages.
However, U.S. Pat. No. 4,371,433, is not practical. In order to effectively prevent leakage of electrical energy, the grommet needs to be attached to each of the terminal plates, the insulating plates, and the end plates. Therefore, a large number of grommets are required, and the overall cost of the fuel cell is large.
The entire terminal plate is generally made of a conductive metal, and has a considerably large mass. The terminal plate needs to have at least a certain thickness for preventing losses due to electrical resistance in collecting electrical energy from the terminal plate. Consequently, the terminal plate has a large mass, and the fuel cell including the terminal plate is heavy.